The invention relates to a method and a grinding machine for the complete grinding of short and/or rod-shaped workpieces that have a non-circular cross-section that is formed by straight and/or curved lines and that have flat end faces that run parallel to one another and relates to a grinding machine in which two grinding spindles are arranged in tandem and that is particularly suitable for performing the method.
The phrase “short and/or rod-shaped workpieces” means that the only workpieces intended are those that do not require machining with an adjustment of the grinding wheel in the Z direction, e.g. the longitudinal direction of the workpiece, or that require only a minor adjustment in the Z direction, perhaps for producing a bevel in the area of the end faces. Thus the grinding wheels are positioned only in the X direction that is perpendicular thereto. In any case, the workpieces have two end faces that are parallel to one another and one exterior contour that is preferably perpendicular thereto and has the length “L”, it being possible for the length “L” to be greater or smaller than the effective diameter of the end face. Thus both rod-shaped and disk-shaped workpieces are included and they can have any desired cross-section/exterior contour. “Rod-shaped workpiece” shall be used in the following for the sake of brevity, disk-shaped workpieces also being included.
One preferred exemplary application for such short, rod-shaped workpieces is mechanical positioning, switching, and control devices in which rod-shaped parts are actuators that transfer movements and forces. In this case, the rod-shaped workpieces can have a length between preferably 10 and 80 mm and a square cross-section with an edge length between preferably 2 and 15 mm. The material can be different metals, but can also be ceramic materials. With appropriate guidance, the non-circular cross-section means that when installed the rod-shaped actuators will move only in their longitudinal direction, but will not turn.
In this type of application, very high demands are placed on the finish-ground rod-shaped workpiece; primary among these are the dimensional accuracy of the basic dimensions, the end faces being parallel, maintaining precisely the right angle between the longitudinal sides and the end faces, the planarity of the end faces, and the maximum roughness Rz.
The accuracy required in specific applications can be attained in that each side of the rod-shaped workpiece is machined individually using horizontal surface grinding. However, this method is limited to geometric cross-sections that have straight edges. In this grinding method, it is very difficult to supply the grinding zone with cooling lubricant due to the surface contact with the grinding wheel. For this reason it is not possible to attain the same material removal rate as with circumferential grinding. In addition, the workpiece must be indexed and reclamped so frequently that economic mass production is not possible. Because of the indexing and reclamping of the workpiece, the tight production tolerances cannot be attained as they can be using the inventive method.
DE 10 2006 007 055 A1 describes a method and a device for machining such workpieces, in which method the workpiece is initially held on its circumference and supplied to a grinding station. Both end faces are simultaneously rough-ground and fine ground there by means of a double wheel. With the double wheel, two coaxial, rotating grinding wheels that are arranged spaced apart from one another grip the workpiece. The grinding wheels have abrasive layers on the interior sides that face one another for rough-cutting and subsequent finish-cutting, and these layers engage one after the other by moving the grinding spindle in the depth direction (X axis). The distance between the finish-cut areas of the grinding wheels is equal to the grinding amount for the workpiece to be machined. Once the end faces have been machined, the workpiece is transferred to a second clamping in which it is clamped by its end faces. Now the exterior contours of the workpiece are produced using non-circular grinding, to which end a second grinding spindle is pivoted into the machining position. The first grinding spindle for the double grinding, which is seated on the same pivotable housing as the second grinding spindle, is pivoted out of the machining area. Once the exterior contour has been machined, the finish-machined workpiece is removed and the next workpiece is moved into position for double grinding the end faces, for which purpose the first grinding spindle must be pivoted back and re-positioned.
In practice it has been found that alternately pivoting and moving the two grinding spindles into the machining position requires a significant amount of time, and no workpieces can be machined during this period. System productivity suffers because of this, which is a major disadvantage, particularly with respect to the generally very large number of workpieces to be produced. The time that cannot be used for grinding and the time in which it is not possible to perform at least some time-parallel grinding can amount to 30% to 50% of the entire machining time for one workpiece.